Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$127.75	5.874%	$135.254	$135.25	$135.25	$135.30
Purchase #2	$103.39	12.471%	$116.2838	$116.28	$116.30	$116.30
Purchase #3	$162.76	4.678%	$170.3739	$170.37	$170.35	$170.40
Purchase #4	$147.93	3.242%	$152.7259	$152.73	$152.75	$152.70
Purchase #5	$220.52	8.398%	$239.0393	$239.04	$239.05	$239.00
Purchase #6	$52.83	12.549%	$59.4596	$59.46	$59.45	$59.50
Purchase #7	$86.92	3.577%	$90.0291	$90.03	$90.05	$90.00
7 purchase totals =	$902.10		$963.1656	$963.16	$963.20	$963.20